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Intel
Improving Energy Efficiency of Computers
Introduction
Over the past fifty years the capability of
computers (often called ‘computing power’)
has increased dramatically while the physical
size and electrical power requirements have
decreased.
The lesson examines the factors that
determine energy use in computers and the
steps that can be taken to minimise energy
loss and extend battery life.
Background
The invention of the electric battery in 1800 made
it possible to produce a steady electric current
and many people began intensive study of its
effects. The heating effect was quickly noted;
wires carrying large electric currents could even
melt. The chemical effect was also discovered
and applied in electrolysis and
electroplating (1800). In 1820,
while demonstrating the heating
effect of an electric current, the
Danish scientist Hans Christian
Ørsted (Oersted) discovered that
an electric current had a magnetic
effect.
losses due to track resistance are small
compared with the losses in active components
such as transistors and the integrated circuits (ICs
or ‘chips’) that contain them.
Why Do CPUs Become Hot?
In the case of simple circuits power use depends
on the voltage and the current: P=V×I. In digital
circuits power is also used in switching between
different states. This ‘dynamic power’ depends on
the capacitance, the frequency of switching and
the square of the voltage change. CPUs (central
processing units) with more than a 100 million
transistors switching at more than 1 GHz may
dissipate 50 to 100 watts when running at full
power; their average power is generally much
less.
The larger the surface area of components the
more readily they can dissipate heat. Small
components operating at high power are likely to
become quite hot and prone to
malfunction. Cooling can be
achieved by using heat sinks
with fins that increase the
surface area and/or by using
fans. The cooling of CPUs
operating above about 15 W
generally necessitates the use
of cooling fans.
Electrical Resistance
Metals
are
generally
good
conductors of electricity; silver is
the best followed closely by
copper. However, all metals show
some resistance to electric current and this gives
rise to the heating effect. The resistance of a wire
depends on the material, the length of the wire
and its cross-sectional area; long thin conductors
have greater resistance than short thick ones. In
1849 James Joule discovered that the rate at
which heat is produced, (i.e. the ‘power’) is
proportional to the square of the current; this can
be expressed concisely by the equation P=I2R,
where P is the power, I is the current and R is the
resistance.
The components in computers and other
electronic devices are generally mounted on a
‘printed circuit board’ or PCB; the board is a nonconductor but metal tracks (usually of copper) are
included to link the various components together.
Reducing the size of computers involves reducing
the width of the conducting tracks and thereby
increasing their resistance. In practice energy
Processor Heat in Context
Although much attention is
given to CPUs they account for
less than 10% of the average
energy use in most laptop computers. The power
supply and the screen account for about 40% and
the other circuit components account for another
40% (see chart).
Lithography
In the fabrication of high density integrated
circuits, such as microprocessor chips, minute
components are built up layer by layer. An image
(or ‘mask’) of the required circuit is projected onto
a silicon wafer; exposed areas may be either
etched away or built up. This process may have
to be repeated 40 or 50 times in order to produce
all the components, which are mostly transistors,
and interconnections required. This technique is
known as lithography.
The size of components and the spacing between
them has recently been reduced successively
from 65 nm to 45 nm and 32 nm and it is intended
to reduce it to 13.5 nm. Because these distances
are much smaller than the wavelength of visible
light (400 to 750 nm) ultraviolet light (10 nm to
400 nm) is used to project the circuit images.
Domestic Energy Use
Smaller transistors operating at lower voltage
generate less heat. However with smaller gaps
between components leakage currents through
the insulating silicon dioxide layers become more
significant. One way of overcoming this problem
is to use other insulating materials such as
hafnium dioxide (HfO2), zirconium dioxide (ZrO2)
or titanium dioxide (TiO2) to separate the
components.
This
can
reduce
leakage
dramatically.
A computer operating at 100 W for 8 hours a day
would account for 0.6 kW h or about 5% of the
total domestic consumption. This is considerably
less than is used in lighting or television.
Improving Computer Efficiency
Ten years ago the energy use of typical desktop
computers was in the range 70 W to 300 W;
modern energy saving computers operate at
around 50 W. Computer manufacturers are
constantly looking for ways to improve the
efficiency of their products. The most obvious way
of doing this is to choose the most energy efficient
computer parts: power supplies, disk drives,
graphics chips etc.
The energy use of CPUs can be reduced by
varying the CPU clock frequency dynamically.
That means boosting the speed during processorintensive tasks and reducing it when the demand
no longer exists. The ‘clock’ referred to here is not
a clock for telling the time of day. All computer
processes are carried out in sequences of steps;
each ‘step’ takes a single clock cycle of typically
less than a nanosecond, and so the clock
frequency would be more than one gigahertz
(1 GHz).
Battery Power
The usefulness of portable computers is largely
dependent on the battery discharge time; this is
typically about 3 hours but with more efficient
computers and improved batteries this might be
extended to 8 hours.
As batteries discharge a chemical change occurs
in which one substance is oxidised and another is
reduced. In the case of rechargeable batteries
this reaction is reversed when the batteries are
being recharged.
The energy storage capacity of a battery can be
expressed in watt-hours. A 36 W h battery
operating at 3.6 V could deliver a current of 2 A
for 5 hours (3.6 V × 2 A ×5 h = 36 W h).
In Ireland the average domestic electricity use is
about 15 kW h per day, about half of which is for
heating.
What Computer Users Can Do
Computer users can do their bit to reduce energy
use by choosing energy saving hardware and by
utilising the energy saving software options such
as reducing screen brightness or putting the
computer into ‘sleep’ or standby mode when it is
idle for a specified length of time.
Intel
Intel Corporation is the world’s largest
semiconductor company. Founded on July 18th,
1968 as Integrated Electronics Corporation and
based in Santa Clara, California, USA, Intel
makes microprocessors, motherboard chipsets,
network cards and ICs, flash memory, graphic
chips, embedded processors, and other devices
related to communications and computing. Intel
was founded by Robert Noyce and Gordon
Moore, and is widely associated with the
executive leadership and vision of Andrew Grove,
who was Intel’s third employee. Since 1968, Intel
has been dedicated to transforming the world
through technology and today employees over
84,000
people
worldwide
and
operates
approximately 300 facilities in 50 different
countries.
Intel decided to locate a manufacturing facility in
Ireland in 1989 and since then has invested over
6.0 billion Euro in turning the 360 acre (145
hectare) Leixlip stud farm into the most
technologically advanced industrial campus in
Europe. Over the years Intel has continued to
expand and grow its Irish operation with two
manufacturing facilities on the campus, Ireland
Fab Operations, which includes Fab 10 and Fab
14, and Fab 24, which includes Fab 24 and Fab
24-2. These facilities produce the latest
generation silicon microprocessors that power
platforms and technology advancements which
are essential to the way we learn, live and work
today.
You can find this and other lessons on www.sta.ie.
Intel
Improving Energy Efficiency of Computers
Teaching Notes
•
Syllabus References
•
The relevant syllabus references are:
Leaving Certificate Physics
•
Heat capacity, specific heat capacity
Heat transfer:
radiation (p. 29)
Conduction,
convection
and
Potential difference
Electric current
Sources of emf and electric current
Electrical conduction in materials
General Learning Points
The following points can be used to review the
lesson content and to inform discussion.
•
Resistance
Effects of electric current (pp. 34-36)
•
Electromagnetic induction
Alternating current
•
The diode
The transistor
Logic gates (p. 44)
•
Learning Outcomes
On completion of this lesson, students should be
able to:
•
•
appreciated that there are many possible
sources of heat in a computer.
the CPU accounts for less than 10% of the
heat in a typical computer.
the space between components and tracks
within a CPU chip is today much smaller
than the wavelength of visible light.
over short distances (< 30 nm) leakage
currents through insulating layers of silicon
dioxide can be significant.
at higher clock speeds CPU produce more
heat; energy can be saved by reducing the
clock speed when the computer is
performing less demanding tasks
•
In a typical desktop computer the CPU
account for about 7% of the heat loss but
the other chips (e.g. graphics chips)
account for much more (27%).
Over the past few decades the space
between components and tracks in a CPU
chip has been gradually reduced from more
than 1000 nm (= 1 μm) to less than 20 nm.
Over short distances (< 30 nm) leakage
currents through insulating layers of silicon
dioxide (SiO2) can be significant; other
insulators are now being used
The switching of millions of transistors
within requires energy; the faster they
switch the more they use. Energy can be
save in computers by reducing the
computer clock frequency when the
computer is performing less demanding
tasks.
In the fabrication of CPUs the very small
component spacing poses particular
challenges. Ultra violet light is used in the
lithography process because it has shorter
wavelength than visible light and so finer
details can be projected and etched.
Intel
Improving Energy Efficiency of Computers
Student Exercises
Student Activities
To investigate the variation of current (I) with
pd (V) for
(a) metallic conductor (a wire-wound 100 ohm,
5 W resistor would be very suitable)
(b) filament bulb (use a 6 V, 300 mA bulb)
(c) copper sulfate solution with copper
electrodes (use 200 mL water, 40 g CuSO4,
10 ml concentrate sulphuric acid and 10 ml
ethanol)
(d) semiconductor diode (e.g. 1N4002)
True/False Questions
a)
b)
c)
d)
e)
Introduction
The neatest way to carry out these experiments is
to use a datalogger with voltage and current
probes. (If you do not have a current probe then a
second voltage probe can be used if placed
across a suitable series resistor).
f)
g)
h)
Procedure
Set up a circuit shown in the diagram. Appropriate
datalogger probes can be attached in place of the
ammeter and voltmeter. The voltmeter and
ammeter should be set to measure appropriate
values (e.g. 0 to 10 volts and 0 to 2 amperes).
Set the datalogger to take a measurement every
second. Set the voltage to zero. Start the
datalogger and then slowly raise the voltage. Do
not allow the current to go too high (200 mA for
the resistor, 300 mA for the bulb, 500 mA for the
copper sulfate or less if the plates are small, and
1 A, 1000 mA, for the diode.)
Stop the datalogger and plot graphs of current
versus voltage.
Note: In the case of the diode the current will rise
very quickly once the voltage goes beyond about
0.8 V so be careful!
The
important
thing to observe is
that the current is
proportional to the
voltage only in the
case
of
the
metallic conductor
(wire-wound
resistor) and then
only if the temperature is constant.
i)
j)
The rate of heat loss in electrical
conductors is proportional to the square of
the electric current.
The clock frequency in a modern CPU is
about 100 kHz.
The technique used in the fabrication of
microprocessors is called lithography.
The distance between ‘components’ in an
integrated circuit is typically about 750
nanometres.
The energy storage capacity of a laptop
battery is about 1.5 kilowatt hours (kW h).
When a computer is turned off it uses less
power than it does in stand-by mode.
The main source of heat loss in a laptop
computer is the CPU.
The magnetic effect of an electric current
was discovered by in 1820 by Hans
Christian Ørsted (Oersted).
All metals show some resistance to electric
current.
The power supply and the screen account
for about 40% of the heat loss from a
typical laptop computer.
Check your answers to these questions on www.sta.ie
Examination Questions
Leaving Certificate Physics (OL) 2006, Q. 12d
A semiconductor material can be doped to form a
p-n junction (semiconductor diode). Explain the
underlined terms. Name a material used as a
semiconductor.
The circuit diagram shows two semiconductor
diodes and two
bulbs, labelled A
and B, connected
to a 6 V d.c.
supply. What is
observed when
the switch is
closed?
Explain why?
Did You Know?
Of the 92 naturally occurring elements most are
metals and are quite good conductors. On the
Periodic Table of Elements the non-metals are
found on the right hand side, towards the top and
many of them are gases. The solid non-metals
are generally poor conductors.
In between these two groups there are seven
elements that have intermediate characteristics: B
(Boron), Si (silicon), Ge (germanium), As
(arsenic), Sb (antimony), Te (tellurium) and Po
(polonium). Although carbon has a conductive
and a non-conductive form (graphite and
diamond) it is generally not regarded as a
semiconductor.
If tiny traces of certain elements are added to
silicon its conductivity increases dramatically; the
silicon is then said to be ‘doped’.
Doping silicon with arsenic (As) at 10 ppm (10
parts per million = 0.001 %) can increase it
conductivity thousands of times.
Doping silicon with phosphorus (P) can change
the conductivity by the same amount. However if
a piece of each of these two types of doped
silicon are joined it is found that electricity can
flow through the junction in only one direction; it is
a solid-state diode.
Biographical Notes
Russell Shoemaker Ohl (1898 – 1987)
Russell Ohl was born in January, 1898, near
Allentown, Pennsylvania.
He entered Pennsylvania State University at the
age of 16. He made a particular study of vacuum
tubes; these had been in use from about from
about 1904 to detect radio signals.
In 1927 Ohl began working at Bell Labs. He
suspected that semiconductors might make better
diodes than the cumbersome vacuum tubes of the
time. Despite scepticism on the part of the
management he persisted and eventually
succeeded. He tried to produce very pure crystals
of silicon. He realised that slight amounts of
impurity had a dramatic effect on their
conductivity. He discovered by accident that two
pieces of silicon with different kinds of impurity
could form a junction that behaved as a diode. In
the process he also developed a photo-diode; he
had noticed that a particular diode behaved
erratically and realised after a few hours that light
affected it. The photo-diode is the basis of today’s
photo-voltaic generators.
Among the few co-workers who understood his
work was Walter Brattain who, along with John
Bardeen and William Shockley, invented the
transistor in 1947.
Following his retirement in 1958 he continued
working and publishing papers on semiconductors
and how to grow crystals with the desired
characteristics. He died in 1987 aged 89.
Revise the Terms
Can you recall the meaning of the following terms?
Reviewing terminology is a powerful aid to recall and
retention.
battery,
capacitance,
computing
power,
conductors, CPU clock, electric current,
electrolysis, electronic, electroplating, etched,
fabrication, frequency, GHz, heat sink, heating
effect, integrated circuit, kW h, lithography,
magnetic effect, microprocessor, oxidised, PCB,
power, power supply, rechargeable battery,
reduced, resistance, silicon wafer, standby mode ,
transistor, watt, watt-hours, wire
Check the Glossary of Terms for this lesson on
www.sta.ie